1. Field of the Invention
The present invention relates to an image forming device which records images on sheets of recording media (papers or the like of predetermined sizes), and to a sheet supplying device which conveys sheets one-by-one from a stack of sheets.
2. Description of the Related Art
Generally, in an image forming device such as a copier or a printer or the like, images are formed on recording media sheets in an image forming section. These sheets are stacked in a sheet supplying device which is provided within the image forming device, and are successively supplied from the sheet supplying device to the image forming section.
As shown in FIG. 16, a sheet supplying device 100 has a presser plate 102 on which sheets (recording media) are placed. The presser plate 102 is urged upward by a coil spring 104. Above the presser plate 102, a supporting shaft 106 is supported so as to rotate freely with respect to a main body frame 130 (not all of the main body frame 130 is illustrated). A feed roller 108, which is half-moon-shaped and conveys the sheets, is fixed to the supporting shaft 106. Core rollers 110 are attached to the both sides of the feed roller 108. The core rollers 110 rotate in a state of contacting a separating pad 112 provided at the main body frame 130.
Cams 114 are fixed to the both end portions of the supporting shaft 106. The cams 114 abut rollers 124 provided at flanges 122 which project from the both side portions of the presser plate 102.
A driven gear 116 is attached to one end portion of the supporting shaft 106. A portion of the peripheral surface of the driven gear 116 is cut out. A driving gear 118, which is driven to rotate by a motor (not illustrated), is meshably disposed at the lower side of the driven gear 116. The driving gear 118 meshes with the driven gear 116 at a predetermined timing so as to transmit the driving force of the driving gear 118 to the driven gear 116, such that the supporting shaft 106 can rotate one time.
As shown in FIG. 17A, at times other than when sheets are being fed, the portions of the cams 114 where the eccentric radii are large abut the rollers 124 of the presser plate 102, and press the presser plate 102 downward in a direction resisting the urging force of the coil spring 104. At this time, the sheets stacked on the presser plate 102 are set apart from the feed roller 108.
As shown in FIG. 17B, when the cams 114 rotate in the direction of the arrow due to the rotation of the supporting shaft 106, the rollers 124 rotate while abutting the cams 114, and the presser plate 102 is pushed upward by the urging force of the coil spring 104. The feed roller 108 and the core rollers 110 also rotate together with the rotation of the supporting shaft 106.
As shown in FIG. 17C, when the cams 114 rotate further in the direction of the arrow, the rollers 124 move along the cams 114, and the presser plate 102 is gradually pushed upward. As shown in FIG. 17D, the presser plate 102 rises to the position at which the rollers 124 abut bearing portions 114a of the cams 114. At this time, the topmost portion of the stack of sheets stacked on the presser plate 102 contacts the feed roller 108, and the sheets are fed out as the feed roller 108 rotates. Conveying, in an overlapping manner, of the sheets which are fed out is prevented by the friction with the separating pad 112.
When the cams 114 rotate further, the presser plate 102 is pushed downward in the direction of resisting the urging force of the coil spring 104, and the cams 114 rotate one time. In this way, the presser plate 102 is lowered to the position shown in FIG. 17A. (See, for example, Japanese Patent No. 2619959.)
In the sheet supplying device 100 shown in FIG. 16, the presser plate 102 is moved upward and downward by the rotation of the cams 114 provided at the supporting shaft 106 of the feed roller 108, and feeding of the topmost sheet of the stack of sheets is carried out. However, when an attempt is made to increase the accommodating capacity (the feeding capacity) of the sheets stacked on the presser plate 102, a problem arises in that the cams 114 inevitably become large.
Namely, in the feeding operations shown in FIGS. 17A through 17D, when the presser plate 102 is raised, the topmost portion of the stack of sheets is pressed by the feed roller 108 and feeding is carried out. When the presser plate 102 is lowered, the topmost portion of the stack of sheets is moved away to a position at which it does not contact the feed roller 108. Accordingly, when an attempt is made to increase the sheet accommodating capacity, the stroke of the presser plate 102 must be made to be large, and the cams 114 become large. Namely, there is the relation that the size of the cams 114 which move the presser plate 102 upward and downward determine the sheet accommodating capacity. Accordingly, a way to satisfy the antithetical needs for an increase in the sheet accommodating capacity and a decrease in the overall size of the device is desired.